Protective immunity to the pathogenic fungus, Histoplasma capsulatum (Hc), requires collaboration between T cells and professional antigen presenting cells such as macrophages and dendritic cells. T cells exert a crucial role in host resistance by releasing cytokines that arm phagocytes to express anti-Hc activity. We reported that one antigen from Hc, recombinant heat shock protein (rhsp) 60, is immunogenic in murine models of histoplasmosis. We also have shown that the protective activity of this antigen requires the presence of CD4+, Vbeta8.1/8.2+ T cells and interferon-gamma, and interleukins-10 and 12 during the inductive phase of vaccination. In the efferent phase, interleukin-12 and interferon-gamma are required as well as CD4+ and CD8+ cells. Protection conferred by rhsp 60 is mediated by a domain spanning amino acids 172-443, and the effect of this polypeptide is dependent on the presence of Vbeta6+ cells and IFN-gamma. Furthermore, our preliminary data indicate that effect of rhsp 60 as vaccine persists for greater than or equal too 3 months and sustaining its durability requires tumor necrosis factor (TNF)-alpha and granulocyte-macrophage colony stimulating factor (GM-CSF) but not interleukins-10 or -12 or interferon-gamma. These data indicate that the requirements for maintaining effectiveness of rhsp 60 shift following the termination of vaccine delivery. The hypotheses are 1) the protective action of rhsp 60 is localized to a peptide, 2) the lack of endogenous IL-10 alters efficacy of rhsp 60 by subverting the generation of either cellular or molecular mediators of protection, and 3) the durability of rhsp 60 vaccination is dependent on TNF-alpha and GM-CSF and that the absence of these cytokines alters the mediators of protection. In this proposal we will pursue three specific aims intended to enhance knowledge regarding the mechanisms of vaccine efficacy using rhsp 60 as a model antigen. In the first aim, we will endeavor to identify a peptide within the protective domain, known as F3 that spans amino acids 172-443. We will seek to determine if a peptide can mimic the activity of F3, if protective T cells emerge and if interleukin-4 may be required for the Th1 response. In addition, we will ask if the peptide can mediate protection in a host with a biased Th2 phenotype. In the second aim, we will seek to understand how IL-10 contributes to vaccine efficacy. We will pursue the possibility that the absence of IL-10 alters cytokine production, antigen presenting cell function, T cell repertoire, and/or the generation of memory/effectors cells. In aim 3, we will examine how the absence of TNF-alpha and GM-CSF alters the durability of the efficacy of rhsp 60 as a vaccine. We will determine if the absence of either of these cytokines alters production of cytokines necessary for protection or causes up regulation of cytokines involved in exacerbating disease. We also will examine if their absence causes alterations in the emergence of protective T cells and/or memory/effectors cells. These studies should provide new insights into the mechanisms that underpin the efficacy of a vaccine. rhsp 60 serves as a paradigm, and the data emerging from this proposal may be broadly applicable to other antigens against intracellular pathogens.